The present disclosure is directed to a flow diffuser and especially one to be used with pipelines of substantial length. When a pipeline extends several miles in length, it is not uncommon for dense liquids to settle. A typical long distance petroleum product pipeline is normally connected to a number of gathering lines which extend into a field having a number of producing wells. Each well normally produces a flow of petroleum products of densities or weights from a well. In addition, the well will typically produce a little or perhaps more than a small portion of water, and also perhaps sand or other types of sediment. Typically, a producing well is connected from the well head to a separator. A simple separator is normally a tall, relatively narrow storage tank. The storage tank sometimes called a shot gun tank. The produced petroleum products are stored in the tank for an interval. This permits sand and other sediment to collect on the bottom. In addition, any water that is mixed in the produced oil will collect at the bottom and petroleum products of less density will float on top of the water. The oil that is produced is taken from the shot gun tank near the top so that the water and sediment is left in the tank. Later the water and sediment are removed from the bottom of the tank for disposal. As a generalization, this separation process does reduce the amount of water. That is, the water is separated and is not delivered in the pipeline. Some wells produce a flow of oil and gas. The gas cut oil tends to froth and is therefore lighter and sometimes will entrain water droplets in the oil. It is also possible for minerals mixed in the oil or water to act as a detergent, thereby breaking down the surface tension and tending to emulsify the oil with water. For a variety of reasons, water is found in produced oil in some quantity. Indeed, where a number of wells connect together from an unmanned field, the amount of water which is delivered with the petroleum products can become unacceptable eventually.
The produced oil commingled with the water droplets as delivered to the pipeline is required to flow many miles in the pipeline. Especially where the fluid flow becomes fairly constant and the pipeline is substantially straight with-modest turns or obstructions, the fluid flow tends to be laminar with a minimum of turbulence. As turbulence is reduced, stratification occurs in the pipeline. Stratification is accompanied by a settling of sediment and water which are carried in the flowing oil. While the sediment may fall out and not move at all, the water tends to flow along the pipeline stratified across the bottom of the pipeline as a results of the differences in density. The denser water settles and flows along the bottom of the pipeline. The denser water is a source of inefficiency in pipeline operation. Water has no heat value and is therefore not worth pumping. While it will be delivered by the pipeline along with the more valuable petroleum based products, the water discounts the value of the petroleum products delivered through the pipeline.
Pipeline products are sold by volumetric calculations. This requires some type of flow meter to determine the fluid flow throughput of a pipeline. Stratification of the fluid flow in the pipeline poses a problem. While major efforts are made to limit the intrusion of water in the flowing products, nevertheless, some water will be captured in the fluid flow and will distort the value and usefulness of a liquid products. Water has absolutely no value. Generally, pipeline products are sold by volumetric measure. The volumetric sale transaction cannot be implemented without knowing the percentage of water that is in the flowing liquid products. When the water stratifies and collects along the bottom, it normally passes beneath or under any sampling device. A sampling device is normally needed to assay the nature of the liquid products flowing in the pipeline. The assay is particularly determined by collecting samples periodically, delivering the samples to a laboratory, and measuring the sample for heat content or some other parameter. The water mixed in the pipeline must be taken into consideration. If the water stratifies and flows beneath the sampling device it will not be sampled. Nevertheless, the water flows through the flow meter and is registered falsely, that is, the flowing water adds to the total throughput while it is not observed by the sampling device.
While the flow meter responds to the entire flow in the pipeline, the sampling device normally is positioned near the central or axial position of the pipeline. The sampling device is operated periodically to take a measured sample. For instance, a sample of 100 milliliters might be collected once per hour. The samples for an interval are collected in a separate container and are removed in that container to be carried to a testing laboratory. The testing laboratory provides an assay for the liquid flowing along the pipeline. The output data is used in determining the value of the liquid product. Assume for instance that the volume of the tested sample is overstated by one percent of valuable hydrocarbon products and is understated by one percent water. While that seems to be a trivial error, it is not uncommon for pipelines to deliver as much as 100,000 barrels per day. An error of one percent in a fluid flow throughput of 100,000 barrels per day is 1000 barrels. Assuming a value of about $20 per barrel, this represents a daily error of $20,000. That is, the purchaser is overpaying by that amount. Restated, the seller is receiving that sum of money for selling water.
The present apparatus is a system which is intended for use with a pipeline and more particularly an apparatus for redistributing stratified liquids flowing in the pipeline. While the water normally tends to settle at the bottom because of differences in density including the phase separation, the present system redistributes the water flowing along the bottom so that droplets of water are able to commingle with the flowing liquid.
An important aspect of the present disclosure is the necessity of accounting for all of the liquid delivered through the pipeline. Even though stratification may occur, the invention mixes valuable hydrocarbon components with entrained water. A mix of valuable hydrocarbons with water (pure or with salt) gives rise to a need for accounting for these. On the other hand, a portion of the liquid may be water which has no value. Restated, it has no BTU content. It is therefore necessary to change the location of sampling devices to assure that the sampling device is exposed to a mix of all constituents including the hydrocarbons and water. Since the pipeline is substantially long, the water always collects at the bottom. This locates the water excessively low for measurement. As noted, a sampling device is installed in the pipeline to take periodic samples which are then processed in a lab to provide an assay of liquid delivered by the pipeline. The sampling device must be axially positioned. If it is positioned relatively high in the pipeline, it will assuredly capture little water. If it is placed excessively low in the pipeline, the data will be skewed by capturing excessive water. There is an optimum location for the position of the sampling device, but that cannot be known because it varies dynamically with the extent of water in the hydrocarbons in the flow. Also, the optimum position will vary in a way that is dependent on production, and is also dependent on environment conditions. It is impossible to know or fix the optimum location. The sampling device typically is therefore located near the centerline axis position of the pipeline. There, it is intended to capture a representative flow, a truly representative sample. In fact, if water stratification occurs, a sample taken from the centerline axis position by the sampling device will not be representative.
The present disclosure sets forth a diffuser mechanism which assures that a representative sample can be obtained. The structure of the present disclosure sets forth a passive device which achieves mixing to reduce water stratification. Indeed, it is passive in the sense that it relies on fluid flow through the pipeline. As stratification occurs, water droplets collect along the bottom of the pipe. Water droplets on the wall of the pipe gravitate to form a water pool at the bottom. The water pool however ordinarily is not stationary. Water moves along the pipe in the form of droplets or a small stream. Because a cross country pipeline has many long straight portions, the liquid stays low along the pipeline.
As many droplets collect along the bottom, they form a flowing stream of water. The width and depth are determined by the size of the pipe and the volume of water collected in the bottom of the pipe. The present apparatus is intended for use with a pipeline which distributes the water in droplet form back into the flowing petroleum. While the water may have an instantaneous velocity which is less than the average velocity, when it is entrained as a droplet, it tends to flow at approximately the same velocity. Moreover, entrained droplets scattered through the flowing petroleum tend to establish an equilibrium. As the surface area of the water droplets is increased, mixing is enhanced, and the present apparatus is a system which accomplishes that. As will be detailed hereinafter, the device of the present system utilizes a number of small tubes which are located in a group or cluster in the pipeline to accomplish the distribution of water liquid into entrained droplet form at various elevations in the pipe, thereby reassuring a fair sampling process.
The following patents were located by a search:
______________________________________ U.S. Pat. No. Patentees ______________________________________ 3,582,048 Sarem 3,583,678 Harder 3,860,217 Grout 4,403,517 Thomte 4,494,413 Bukkems, et al 4,971,450 Gerich ______________________________________
U.S. Pat. No. 3,582,048 discloses a mixing conduit. It is installed in a system which cannot handle 100% of the volumetric capacity.
U.S. Pat. No. 3,583,678 is similar to the prior reference in that it shows in various views a full scale pipeline which is partly plugged by the transverse structures. While it is more like a geometry dissertation, it cannot provide a structure of any significance to pipeline mixing equipment in conjunction with a downstream measuring device.
U.S. Pat. No. 3,860,217 is a type of mixing device, note the sectional views of FIGS. 3, 7, 9, etc. It is somewhat remote compared to the earlier two references.
U.S. Pat. No. 4,403,517 shows an insert 11 in the pipe 5 which is a static vane mixer having fixed blades to cause turbulence, note Column 3.
U.S. Pat. No. 4,494,413 discloses a sampling apparatus for handling a flow of stratified fluid, note the background discussion in Column 1. If anything, this is an expensive system which provides a very extravagant answer to the problem.
U.S. Pat. No. 4,971,450 shows a solid body which blocks flow. It is limited in volume.